Influencing Factors and Solutions to Excessive Residues of Dry Composite Solvents

Solvent residue exceeding the standard is often encountered in the production of soft packages, especially in dry lamination production. If the solvent residue is not properly controlled, it may affect delivery, or in severe cases, it may cause the loss of customers and even require a large amount of compensation. Therefore, in daily production, enterprises should pay attention to the following influencing factors and make corresponding process adjustments to ensure that the residual value of dry composite solvent can meet the standards.

1. Raw materials

Compared with PET structure, BOPP is less easy to control solvent residue during production, whether in the printing process or the laminating process. First, let’s analyze the molecular structure of the material. The density of BOPP is 0.96g/cm3, and the density of PET is 1.38g/cm3. Compared with PET, BOPP material has low density and large intermolecular gaps. It is easy to absorb ink and glue during the printing composite process. The solvent is not easily released after adsorption, resulting in varying degrees of solvent residue exceeding the standard in the printing and lamination processes.

Different film substrates use the same inks and adhesives during gravure printing and dry lamination, and the production process is also the same, but the residual solvent content of the products will be different. This is due to the adsorption of solvents by different film substrates. Not the same as the release rate.

The release rate of ethyl acetate from commonly used film substrates is: PET>PA>BOPP (the adsorption rate is opposite). Usually the temperature of the drying oven for printing and lamination is close to the melting point of the BOPP film, and its molecules move more irregularly, and the adsorption rate of solvents such as ethyl acetate and toluene is accelerated. Therefore, for BOPP films, it is more difficult to further reduce the residual solvent content.

2. Printing process

The drying oven temperature of the BOPP structure is low during the printing process, and excessive speed can easily cause excessive melt residue during the printing process.

The improvement method is to reduce the printing speed and extend the residence time of the printing film in the drying box. The printing film is fully dried to reduce the solvent residue. Usually, it is necessary to ensure that the solvent residue is less than 2mg/m2 after the printing film is removed from the machine to facilitate the production of the composite process. .

3. Key points of composite process control

The temperature of the drying oven should not be too high in the first section: if there are two sections of drying oven (such as BOBST high-speed laminating machine), the temperature of the first section should be controlled at 70~75℃, and the second section should ensure that the printed film is not stretched. , try to increase the temperature. In China, there are generally dry laminating machines with three or four stages of drying ovens. The temperature of the drying oven follows a gradient setting. The air volume and temperature of the first stage drying oven must be controlled well. If the temperature entering the drying tunnel is too high at the beginning and the drying is too fast, the solvent on the surface of the glue layer will evaporate quickly, resulting in a local increase in the concentration of glue on the surface layer, and the internal solvent will be trapped inside. After passing through the subsequent oven, the solvent will evaporate slowly. The internal solvent cannot be fully evaporated.

BOPP is a material that has a strong adsorption capacity for solvents. The greater the amount of glue applied, the more serious the solvent residue will exceed the standard after compounding. This can reduce the amount of glue applied to reduce solvent residue. Use a 140 or 150 line rubber coating roller to do 36% to 38% high concentration coating to reduce the adsorption of solvent by BOPP, and appropriately reduce the amount of glue applied to 2.5~2.6g. /m2, which can effectively reduce the solvent residue in the composite process.

4. On-site process adjustment

If the customer does not use high-line-count screen rollers for high-concentration coating to reduce the residual amount, they can reduce the pressure of the glue coating roller, increase the scraper pressure, increase the scraper angle, and reduce the compounding speed. This method can appropriately reduce the amount of glue applied, prolong the residence time of the glued film in the drying box, and also reduce solvent residue.

5. Conclusion

In short, the solvent residue in the printing film is controlled below 2mg/m2, and the total solvent residue after lamination is controlled below 5~8mg/m2. Then after the product is placed in the curing room for curing, the solvent residue can be controlled below 5mg/m2. Meet customer needs and meet international standards.